Re: [HACKERS] Function to move the position of a replication slot

On 2017-08-16 21:25:48 -0400, Robert Haas wrote:
> On Wed, Aug 16, 2017 at 5:55 PM, Andres Freund <andres@anarazel.de> wrote:
> > I think we should constrain the API to only allow later LSNs than
> > currently in the slot, rather than arbitrary ones. That's why I was
> > thinking of "forward".  I'm not convinced it's a good / safe idea to
> > allow arbitrary values to be set.
>
> Maybe I shouldn't play the devil's advocate here, but isn't a feature
> like this by definition only for people who Know What They Are Doing?
> If so, why not let them back the slot up?  I'm sure that will work out
> just fine.  They Know What They Are Doing.

I have yet to hear a reason for allowing to move things backward etc. So
I'm not sure what the benefit would be. But more importantly I'd like to
make this available to non-superusers at some point, and there I think
it's more important that they can't do bad things. The reason for
allowing it for non-superusers is that I think it's quite a useful
function to be used by an automated system. E.g. to ensure enough, but
not too much, WAL is available for a tertiary standby both on the actual
primary and a failover node.